Chromium and Ziegler-Natta polymerization catalysts have been known since the 1950's. Thermally activated chromium catalysts were disclosed in U.S. Pat. No. 2,825,721 and are commonly referred to as Phillips catalysts. Catalysts containing chromium may also contain additional components such as titanium, aluminum, boron, and vanadium, as disclosed in U.S. Pat. No. 4,303,770.
Ziegler-Natta catalysts can be broadly described as consisting of combinations of strong reducing agents, such as an organometallic compound of an alkali metal or an alkaline earth metal (such as aluminum and magnesium), in combination with various reducible heavy metal compounds, such as the halides and alkoxides of the metals in Groups IVB, VB, and VIB of the Periodic Table. Ziegler-Natta catalysts are commonly supported on MgCl.sub.2, but silica-supported Ziegler-Natta catalysts are also known.
Other types of silica-supported Ziegler-Natta catalysts which are known in the prior art include:
A. The multiple site type, for example, the catalysts disclosed in U.S. Pat. No. 5,155,079, which discloses a zirconium compound and a vanadium or titanium compound deposited on silica particles;
B. The metallocene type compounds in which the transition metal compound, a bis (cyclopentadienyl) metallocene, especially a zirconocene, as disclosed in U.S. Pat. No. 4,701,432, or a monocyclopentadienyl compound of zirconium, hafnium, or titanium, as disclosed in U.S. Pat. No. 5,057,475; and
C. Catalysts for isotactic propylene as in U.S. Pat. No. 4,950,631.
U.S. Pat. No. 3,787,384 discloses catalyst synthesis by reaction of silica with an organomagnesium compound and subsequent treatment of the product with titanium tetrachloride. The particulate catalyst that is obtained is activated with an aluminum alkyl cocatalyst. U.S. Pat. No. 3,748,539 discloses a similar use for silica in catalyst synthesis, but the silica particles are first modified by reaction with an organoaluminum compound, and the transition metal is vanadium. U.S. Pat. No. 4,808,561 discloses a silica-supported metallocene catalyst prepared by reaction of methylaluminoxane with silica, followed by treatment with a zirconocene. In all of these disclosures, the porous silica is of relatively low pore volume, surface area, and surface functionality.
U.S. Pat. No. 4,701,432 (mentioned above) discloses an olefin polymerization catalyst comprising (a) a supported transition metal containing component comprising the support treated with at least one metallocene and at least one non-metallocene transition metal compound, and (b) a cocatalyst comprising an aluminoxane and an organometallic compound of a metal of groups IA, IIA, IIB, or IIIA of the periodic table. Although the patent discloses a support of an inorganic oxide with surface areas of between 50 to 1000 m.sup.2 /g and a pore volume of between 0.5 to 3.5 ml/g, the patent mentions that the specific particle size, surface area, pore volume, and number of surface hydroxyl groups are not critical to the patent's utility.
U.S. Pat. No. 5,232,883 discloses a process for obtaining high surface area silica particles with catalysts supported thereon. The process includes the step of spraying an electrostatically charged gellable liquid material into a chamber to produce macrodrops within which gelling is produced after spraying. The process of the '883 patent is utilized only with chromium-containing catalytic components.
U.S. Pat. No. 4,791,089 discloses a method of preparing a high pore volume, medium surface area zirconia-titania-silica tergel useful as an olefin polymerization or co-polymerization catalyst support. In particular, this patent discloses a pore volume in the range of about 1.5 to 3.5 cc/g and a surface area in the range of about 200 to 600 m.sup.2 /g.
In olefin polymerization, it is desirable to develop a catalyst with high activity which produces polymers with high bulk density and good morphology.